Just a quick question. I am looking at the 03 700/600's. The call it a parallel twin cyclinder even fire. I could use a littl eexplanation of exactly what this even fire means. Does it mean both cylinders fire at the same time?

Thanks For Any Enlightenment

 

Even firing means the cylinders fire at even intervals.

A four stroke cylinder fires once every 720 degrees of crank rotation. An even firing two cyl therefore has the first cyl firing at 0degrees, the the second at 360. (0,360, 720, and so on)

Firing Odd is not bad, it just doesn't sound as smooth. If your ear is tuned, you can pick an odd firing 2cyl out of a crowd. No car or truck that I have ever heard of has ever been odd firing. This is only a 2 cylinder thing.

The reason the V is used in street bikes (and my ATV) is mainly reduced vibration.


-The inline 2 is the worst vibrator of the 2cylinders, most compact, but fires even. Both pistons have to move up and down at the same time in order to fire this way. Most compact 2 cyl.

-The 45V has a little reduced vibration, some fire even, some fire odd (harley). Very compact.

-the 90V has VERY MUCH less vibration than the 45V and the inline 2 when configured like the Prairie650, but it fires odd 0, 270, 720 etc. Not as compact as the above 2 motors.

-The horizontally opposed 2 cylinder has extremely much less vibvration than any other 2 cyl, and is even firing. Worst motor for taking up space.

2 cylinders are always better than one. One will vibrate the most, and have the biggest torque pulses. One large piston has greater thermal expansion variation between the piston and cylinder.

2 cyls are worse to work on. You have to adjust, machine, replace, and tweak twice as many things.

 

NYROC,
Are you sure you know what your talking about? Polaris says that the 600/700 Sportsman motor fires even as in both cylinders move up an down together and fire at the exact same time resulting in a more "single cylinder like" action. They say it is done for the better torque characteristics.
Also, you didn't say that an inline (or parallel) twin can't have pistons moving in opposite directions did you. Because Yamaha made the XS650 motorcycle which fires uneven with a 360 degree crank and the TDM850 which fires uneven with a 270 degree crank.
Just my 2 cents,
Polzook

 

NyRoc is correct. And very well said. Two stroke twins have pistons which oppose each other, one going up while the other goes down. I don't know of any exceptions to the twin cylinder inline four-stroke being even firing, with the pistons going up and down together, but firing on opposite strokes. This is how they are able to share a carbureator easily.
I don't know about the Yamahas that Polzook brought up...

 

The engine is what it is .
Both cylinders fire together. instead of one piston there are two, and they travel up and down together fireing on both sides at the same time.
Thats why it has such awsome torque.

 

No, that is incorrect. The pistons travel up and down together but fire on opposite strokes. This is why a small carb works well, because the intake stroke on one cylinder is happening while the power stroke is happening on the other cylinder, enabling the small carb to fill one cylinder at a time and creating a more constant flow. It is also why there is no vibration advantage over a single without a balance shaft. [img]i/expressions/face-icon-small-cool.gif[/img]